| Hypovolemia | |
|---|---|
| Other names | Oligemia, hypovolaemia, oligaemia, hypovolæmia, volume depletion |
 | |
| A diagram showing the formation ofinterstitial fluid from thebloodstream | |
| Specialty | Emergency medicine |
| Symptoms | Headache, fatigue, nausea, profuse sweating, dizziness |
| Complications | Cardiac arrest,hypovolemic shock |
| Differential diagnosis | Dehydration |
Hypovolemia, also known asvolume depletion orvolume contraction, is a state of abnormally lowextracellular fluid in the body.[1] This may be due to either a loss of both salt and water or a decrease inblood volume.[2][3] Hypovolemia refers to the loss of extracellular fluid and should not be confused withdehydration.[4]
Hypovolemia is caused by a variety of events, but these can be simplified into two categories: those that are associated withkidney function and those that are not.[5] The signs and symptoms of hypovolemia worsen as the amount of fluid lost increases.[6] Immediately or shortly after mild fluid loss (fromblood donation,diarrhea,vomiting, bleeding from trauma, etc.), one may experienceheadache,fatigue,weakness,dizziness, orthirst. Untreated hypovolemia or excessive and rapid losses of volume may lead tohypovolemic shock.[7] Signs and symptoms of hypovolemic shock includeincreased heart rate,low blood pressure,pale or cold skin, andaltered mental status. When these signs are seen, immediate action should be taken torestore the lost volume.
Signs and symptoms of hypovolemia progress with increased loss of fluid volume.[5]
Early symptoms of hypovolemia include headache, fatigue, weakness, thirst, and dizziness. The more severe signs and symptoms are often associated with hypovolemic shock. These includeoliguria,cyanosis, abdominal and chest pain,hypotension,tachycardia, cold hands and feet, and progressively altering mental status.[citation needed]
The causes of hypovolemia can be characterized into two categories:[5]
The signs and symptoms of hypovolemia are primarily due to the consequences of decreased circulating volume and a subsequent reduction in the amount of blood reaching the tissues of the body.[9] In order to properly perform their functions, tissues require the oxygen transported in the blood.[10] A decrease in circulating volume can lead to a decrease in bloodflow to the brain, resulting in headache and dizziness.[citation needed]
Baroreceptors in the body (primarily those located in thecarotid sinuses andaortic arch) sense the reduction of circulating fluid and send signals to the brain to increase sympathetic response (see also:baroreflex).[11] This sympathetic response is to releaseepinephrine andnorepinephrine, which results in peripheralvasoconstriction (reducing size of blood vessels) in order to conserve the circulating fluids for organs vital to survival (i.e. brain and heart). Peripheral vasoconstriction accounts for the cold extremities (hands and feet), increased heart rate, increased cardiac output (and associated chest pain). Eventually, there will be lessperfusion to the kidneys, resulting in decreased urine output.[citation needed]
Hypovolemia can be recognized by afast heart rate,low blood pressure,[12] and the absence ofperfusion as assessed by skin signs (skin turning pale) and/orcapillary refill onforehead,lips andnail beds. The patient may feel dizzy, faint, nauseated, or very thirsty. These signs are also characteristic of most types ofshock.[13]
In children, compensation can result in an artificially high blood pressure despite hypovolemia (a decrease in blood volume). Children typically are able to compensate (maintain blood pressure despite hypovolemia) for a longer period than adults, but deteriorate rapidly and severely once they are unable to compensate (decompensate).[14] Consequently, any possibility ofinternal bleeding in children should be treated aggressively.[15][16]
Signs of external bleeding should be assessed, noting that individuals can bleed internally without external blood loss or otherwise apparent signs.[16]
There should be considered possible mechanisms of injury that may have caused internal bleeding, such as ruptured or bruised internal organs. If trained to do so and if the situation permits, there should be conducted asecondary survey and checked the chest and abdomen for pain, deformity, guarding, discoloration or swelling. Bleeding into the abdominal cavity can cause the classical bruising patterns ofGrey Turner's sign (bruising along the sides) orCullen's sign (around the navel).[17]
In a hospital, physicians respond to a case of hypovolemic shock by conducting these examinations:[citation needed]
Untreated hypovolemia can lead to shock (see also:hypovolemic shock). Most sources state that there are 4 stages of hypovolemia and subsequent shock;[18] however, a number of other systems exist with as many as 6 stages.[19]
The 4 stages are sometimes known as the "Tennis" staging of hypovolemic shock, as the stages of blood loss (under 15% of volume, 15–30% of volume, 30–40% of volume and above 40% of volume) mimic the scores in a game oftennis: 15, 15–30, 30–40 and 40.[20] It is basically the same as used in classifyingbleeding by blood loss.[citation needed]
The signs and symptoms of the major stages of hypovolemic shock include:[21][22]
| Stage 1 | Stage 2 | Stage 3 | Stage 4 | |
|---|---|---|---|---|
| Blood loss | Up to 15% (750 mL) | 15–30% (750–1500 mL) | 30–40% (1500–2000 mL) | Over 40% (over 2000 mL) |
| Blood pressure | Normal (Maintained byvasoconstriction) | Increaseddiastolic BP | Systolic BP < 100 | Systolic BP < 70 |
| Heart rate | Normal | Slighttachycardia (> 100 bpm) | Tachycardia (> 120 bpm) | Extreme tachycardia (> 140 bpm) with weak pulse |
| Respiratory rate | Normal | Increased (> 20) | Tachypneic (> 30) | Extremetachypnea |
| Mental status | Normal | Slight anxiety, restless | Altered, confused | DecreasedLOC,lethargy,coma |
| Skin | Pale | Pale, cool, clammy | Increaseddiaphoresis | Extremediaphoresis;mottling possible |
| Capillary refill | Normal | Delayed | Delayed | Absent |
| Urine output | Normal | 20–30 mL/h | 20 mL/h | Negligible |
The most important step in treatment of hypovolemic shock is to identify and control the source of bleeding.[23]
Medical personnel should immediately supply emergency oxygen to increase efficiency of the patient's remaining blood supply. This intervention can be life-saving.[24]
Also, the respiratory pump is especially important during hypovolemia as spontaneous breathing may help reduce the effect of this loss of blood pressure on stroke volume by increasing venous return.[25]
The use ofintravenous fluids (IVs) may help compensate for lost fluid volume, but IV fluids cannot carry oxygen the way blood does—however, researchers are developingblood substitutes that can. Infusingcolloid orcrystalloid IV fluids also dilutesclotting factors in the blood, increasing the risk of bleeding. Current best practice allowpermissive hypotension in patients with hypovolemic shock,[26] both avoid overly diluting clotting factors and avoid artificially raising blood pressure to a point where it "blows off" clots that have formed.[27][28]
Fluid replacement is beneficial in hypovolemia of stage 2, and is necessary in stage 3 and 4.[21] See also the discussion ofshock and the importance of treating reversible shock while it can still be countered.
The following interventions are carried out:[citation needed]
Vasopressors (such asdopamine andnoradrenaline) should generally be avoided, as they may result in further tissueischemia and don't correct the primary problem. Fluids are the preferred choice of therapy.[29]
In cases where loss of blood volume is clearly attributable to bleeding (as opposed to, e.g., dehydration), most medical practitioners prefer the termexsanguination for its greater specificity and descriptiveness, with the effect that the latter term is now more common in the relevant context.[30]
The term hypovolemia refers collectively to two distinct disorders: (1) volume depletion, which describes the loss of sodium from the extracellular space (i.e., intravascular and interstitial fluid) that occurs during gastrointestinal hemorrhage, vomiting, diarrhea, and diuresis; and (2) dehydration, which refers to the loss of intracellular water (and total body water) that ultimately causes cellular desiccation and elevates the plasma sodium concentration and osmolality.